Nonlinear Analysis of Steel Frames with Ductile Connections

One of the typically damaged steel beam-column connection during the Northridge earthquake of 1994 was bolted-web, welded-flange (BWWF), now known as “pre-Northridge” connection. Proposed post-Northridge connections are more ductile and capable of dissipating more energy, thus improving the behavior of steel moment resisting frames (SMRF). The post-Northridge connections with added ductility will be denoted in the paper as BWWF-AD. However, the estimation of the nonlinear response of SMRF in the presence of BWWF-AD is not simple. These are essentially partially restrained (PR) connections. The behavior of PR connections is generally represented by moment-relative rotation (M-θ) curves. Along with material and geometric nonlinearities, the presence of PR connections adds another major source of nonlinearity and must be considered appropriately for accurate seismic response analysis. Structural Seismic Design Associates (SSDA) proposed a unique proprietary SlottedWebTM connection and tested several full-scale models. The nonlinear response of two frames in the presence of BWWF and ductile BWWF-AD connections were calculated and studied. Ten actual recorded earthquake time histories, six of them were recorded during the Northridge earthquake of 1994, were used to calculate the response. Several important observations and design recommendations are made.